Why does Nikon warn about banding at high ISOs when using autofocus on Nikon D4 or D800?

Question

Nikon says that banding may occur at high ISO sensitivities with autofocus on the D4 or D800:

D800

Noise in the form of horizontal lines may appear in pictures taken with AF-S Zoom Nikkor 24-85 mm f/3.5-4.5G (IF) lenses at ISO sensitivities over 6400; use manual focus or focus lock.

D4

Noise in the form of lines may appear during autofocus at high ISO sensitivities. Use manual focus or focus lock. Lines may also appear at high ISO sensitivities when aperture is adjusted during movie recording or live view photography.

What would explain this behavior?

Asked by DragonLord

Answer

This problem is caused by electromagnetic interference generated by the SWM in many Nikon lenses.

There are cases where Canon lenses with USMs have caused banding. See this dpreview forum thread for an instance of sensor banding caused by a USM lens mounted on a Canon DSLR.

Answered by DragonLord

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